More Than Half of Donated Hearts and Lungs Get Thrown Out

But scientists may have discovered a workaround.

Twenty-two Americans die every day waiting for an organ transplant. The number of transplantations is on the rise, but there are some inherent roadblocks in the system, like the fact that organs have a very short shelf life, so to speak: More than 60 percent of the hearts and lungs donated every year have to be discarded because they can't be kept on ice for more than four hours.

Recent estimates found that if even half of these organs were transplanted, the waiting list would disappear within two or three years. (The liver, intestine, and pancreas can last slightly longer without blood flowing; they're usable for eight to 12 hours after recovery from a donor, and kidneys can last up to 36 hours.)

Scientists are looking into the feasibility of tissue and organ banks to solve the problem of discarded organs, but that cryopreservation concept comes with its own set of challenges. Mainly, how can you safely freeze and thaw sizable pieces of human tissue without damaging it? Currently an ice-free process known as vitrification is used to preserve embryos, eggs, and stem cells, but it only works on a small scale. (Samples larger than a few milliliters often crack or crystalize when they're warmed.) A team of researchers from the University of Minnesota thinks they found a solution to the more dicey rewarming step; they used nanotechnology to do it.

For a new study in Science Translational Medicine, investigators showed how they successfully thawed samples without cellular damage via a process called nanowarming. First, they put vitrified tissue (specifically, frozen human skin cells, segments of pig heart tissue, and sections of pig arteries) in a solution that contained silica-coated iron oxide nanoparticles. Then they applied an external magnetic field that made the nanoparticles act as tiny heaters, uniformly warming the sample. They tested the nanowarmed samples for viability and none of the tissues showed signs of harm, unlike controls that were warmed slowly over ice. Then the nanoparticles were successfully washed from the samples after heating. The samples' viability matched or exceeded those thawed using the current gold standard of convective heating.

Past research has shown that nanowarming was effective, but only in solutions of about 1 milliliter. The University of Minnesota team got it to work in 50 milliliters. The plan is to test the technology on rodent organs, then scale up to those from pigs, and, hopefully, humans. It's not a sure thing, but the team is optimistic. "These results are very exciting and could have a huge societal benefit if we could someday bank organs for transplant," senior author John Bischof, a mechanical engineering professor, said in a release.